1. Field of the Invention
This invention relates generally to the measurement of electrical signals and more particularly to a technique for determining the magnitude of a time varying electrical signal.
2. Description of Related Art
A high frequency signal should not exceed the dynamic range of the system in which the signal is processed. Proper adjustment of the system gain depends upon accurately detecting the level of the signal being processed. Prior art techniques included peak detection of the envelope with a slow decay between peaks. One of the disadvantages of peak detection with slow decay is the rate at which the peak detector must increase to a new peak. It must be quicker than the rate at which the peak detector decays between peaks, however the slower decay rate tends to make an accurate acquisition of sharp peaks more difficult. Another disadvantage of this approach is that it supplies no information about the duration of the peaks.
Another prior art technique relies upon the logarithmic nonlinearity of a diode to convert an ac current into a dc voltage. This technique produces a small dc voltage proportional to the mean of the current squared. One disadvantage of this approach is that the typically small dc output is subject to random device mismatch. Another more significant disadvantage of this and similar approaches is that no information is gained regarding the signal peaks.
Accordingly, it is the primary object of the present invention to provide a method and apparatus for measuring the magnitude of an electrical signal.
It is another object of the invention to provide an improvement in measuring the magnitude of a high frequency signal.
It is still a further object of the invention to provide a method and apparatus for determining the degree to which the dynamic range of a system has been exceeded.
The foregoing and other objects are achieved by measuring the percent of time the envelope of a varying modulated signal is above a predetermined programmable threshold. The technique is implemented by means of a level detector including an envelope detector along with means for detecting when the envelope has exceeded the programmable threshold. The output of the level detector is sampled and fed to a counter which provides a digital output which indicates the percentage of time the envelope exceeds the set threshold.
Further scope of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be noted, however, that the detailed description and specific examples, while describing the preferred embodiments of the invention, are provided by way of illustration only, since various changes and modifications coming within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.